Color photography



- tend to occlude the metallic silver and prevent its Patented June 12, 1945 Paul. w. Vittum and Edwin E. Jelley, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., aeorporation of New Jersey .No Drawing. Application November 29, 1941, Se-

- rial No. 421,042. InGreat January 11,

' Claims.

This invention relates to improvements in photographic processing solutions and particularly to solutions designed for removal of metallic silver from, photographic layers.

It is known that in many processes of color photography. both dye images and silver images may be formed in a photographic layer. It is desirable to removethe metallic silver at the end of the process so that a pure transparent dye image remains in the photographic layer. This is generally accomplished by the use of a silver removing bath containing an oxidizing agent for the silver and at the same time or in a subsequent bath dissolving the silver salt thus formed. Silver oxidizing agents ordinarily used are potassium ierrlcyanide or acid dichromate bleaches followed by a silver halide solvent -such as hypo.

It has been found that in some cases the dye or other agents present in the photographic layer being acted upon by the oxidizing agents intended to convert it to a silver salt prior to removal.

.This is especially true in the case oi'emulsions containing an organic solvent for couplers and silver saltsolvent include compounds such 'as D tassium ierricyanide and acid dichromate. To these bleach baths, we add suitable organic solvents in the proper amount. Organic solvents suitable for use according to our invention include monohydroxy alcohols such as benzyl alcohol, isopropyl alcohol, butyl alcohol, s-phenyiethyl alcohol, 'y-phenyl-n-propyl alcohol p-and y-diethylaminopropyl alcohol, s-diethylaminoethyl alcohol, nitroethyl and nitropropyl alcohol, turfuryl alcohol. and tetra-lrvdroi'urfuryl alcohol, and aliphatic ketones sucha's acetone.-

These organic solvents may be used in the bleach bath in quantities ranging from about 1% to about 10% of the volume of the bleach solution. For example. benzyl alcohol may be dissolved in the solution to the extent -of about 1%. isopropyl alcohol to the extent of 5 to 10% and acetone to the extent oi about 5 to 10%. Acetone is preferred for use in acid dichromate bleaches and the alcohols such "as benzyl alcohol appear to give the best results in potassium ierricyanide bleaches.

The following examples illustrate bleach baths dyes such as those described in Mannes a Godow- 6 which may be used according to our invention.

removal of metallic silver from photographic'layers. A further object is to provide a means for 40 the complete removal of metallic silver from emulsion layers containing dyes protected by organic solvents. Other objects will appear from the following description of our invention.

These objects are accomplished by incorporat- 4 ins in the bleach bath which converts metallic silver to a silver salt, an organic solvent such as a monohydroxy'alcohol or an aliphatic ketone. These solvents permit the bleach bath to penetrate any organic material in the emulsion so 60 that the bleach bath is able to talll'c silver therein. v

As stated above, the bleach baths ordinarily act on me- I used for the oxidation oi metallic silver and conine 56 causesthemetallic silver versionoi itto asilver saitpriortorsmoval sky U. 8. Patent 2,304,940, granted December 15, Example 1 1942tar5delley1and Vittum U. S. Patent 2,322,027, Chicane acid (10% solution) 1 gran une 5, 1943. In those processes the a coupler originally present in the emulsion layer U Hydmbmmic 9 and the dye formed from it are dissolved in globom bromide ules of a solvent such as hydrolyzed cellulose acetime hate or tricresyl phosphate which presumably wets water tllie metallic silver as it is formed and thenen- 3 mm 2 coses portions of it which can'no longer be aiiected byaqueous solutions of silver oxidizing 35 g fi mg aggaigam" g 5 ents.

I It is, therefore, an object oi! the present invenm$ figt f'f'f'i 5 tion to provide novelsolutions designed for the ig 00 g: 1

These solutions are followed in each case by the customary solution of hypo or other silver salt solvent such as ammonia, potassium thiocyanate or potassium cyanide.

Our invention is especially useful with oi color photography-such as those described in the Marines t Godowsky "U. 8. Patent 2,304,940

and the Jelley and Vittum U. 8. Patent 2,322,027, referred to above. Those applications describe processes or color photography in which discrete particles of a color coupler and an organic solvent for the ooupler'and for the dye formed therefrom are dispersed in a sensitive silver halide emulsion layer. In some cases the organic solvent used to dissolve the coupler and dye formed from it to be retained in the rescue methods 2 is eilected by the use of our invention.

Our invention is also useful in other methods of color photography such as that "described in Mannes, Godowsky 8r Wilder U. 8. Patent 2252,- 718, August 19, 1941, and in bleach-out methods of color photography, such as that described in- Seymour U. S. Patent No. 2,184,022, December 19,

It will be understood that the modification and examples included herein are illustrativ only and that our invention is to be taken as limited only by the scope or the appended claims.

We claim: 1. The method of removing silver from a photographic layer containing silver and dye in particles of water-permeable solvent insoluble in water above 20 C.,,whiqh comprises oxidizing the silver contained in said solvent to a silver salt in the presence of an organic solvent selected from the group consisting of monohydroxy alcohols and aliphatic ketones, which are soluble in said water-insoluble solvent and removing the silver salt thus formed with a silver salt solvent.

2. The method of removing the silver image from a photographic gelatin layer containing said image associated with dispersed particles of a water-permeable organic compound insoluble in water above 20 0.. which comprises convertin said silver to a silver salt with a solution of a silver oxidizing agent and an organic solvent for said water-insoluble organic compound, said organic solvent being selected from the group consisting of monohydroxy alcohols and aliphatic ketones, and removing the silver salt thus formed with a silver salt solvent.

3. The method of removing the silver image from a photographic gelatin layer containing said image associated with dispersed particles of a water-permeable organic compound insoluble in water above 20 C., which comprises converting said silver to a silver salt with a solution of a silver oxidizing agent and a monohydroxy alcohol which is a solvent for said water-insoluble organic compound, and removing the silver salt thus formed with a silver salt solvent.

4. The method of removing the silver image from a photographic gelatin layer containing said image associated with dispersed particles of a water-permeable organic compound insoluble in water above 20 0., which comprises converting said silver to a silver salt with a solution of a silver oxidizing agent and an aliphatic ketone which is a solvent for said water-insoluble organiccompound,-and removing the silver salt thus formed with a silver salt solvent.

5. The method of removing the silver image from a photographicgelatin layer containing said image associated with dispersed particles of a water-permeable organic compound insoluble in water above 20 C., which comprises converting said silver to a silver salt with a solution of potassium ferricyanide and a monohydroxy alcohol which is a solvent for said water-insoluble organic compound, and removing the silver salt thus formed with a silver salt solvent.

- PAUL W. VITI'I'UM. r EDWIN E. JEILEY. 

